The present invention relates a method of making a resistor and, more particularly, a radiation hard resistor.
Radiation hardened circuits can require high value, e.g., 100,000 ohms, radiation hard resistors to prevent discharge of selected nodes during radiation transients. In order to make a radiation hard resistor, a high doping level is required so that radiation induced carriers are relatively small in number compared to the normally existing carriers. Thus the resistance value does not significantly change during radiation transients. However, a high doping level in a resistive material such as polycrystalline silicon (p-Si) results in a low value of resistivity, e.g., 20 ohms/square, when used with a p-Si thickness of 500-600 nanometers (nm), which is a typical thickness for p-Si gate electrodes and circuit interconnects. Hence a thinner layer of p-Si must be used to achieve the required high resistivity, e.g., 10.sup.4 ohms/square. The resistor area cannot be masked off when depositing the relatively thick p-Si gate electrodes and interconnects since the required high deposition temperatures would destroy the mask.
It is, therefore, desirable tc have a method of forming a relatively high value radiation hard resistor.